N,n-dialkylhydroxylamines as shortstopping agents for emulsion polymerizations



' controllable variation in vulcanization rate.

United States Patent This invention relates to an improved process for shortstopping polymerization processes employing ethylenically unsaturated monomers and deals particularly with those polymerization processes for making synthetic rubber latices.

Synthetic rubber latices are prepared commercially by emulsion polymerization of rubber-forming monomers and the polymerization must be stopped to give a product of desired optimum characteristics. Much study has been made toward finding good shortstops and numerous compounds have been found quite useful. However, the compounds used heretofore have certain disadvantages and are not generally satisfactory with all types of polymerization systems. For example, hydroquinone has been used in hot butadiene-styrene systems, but it does not satisfactorily shortstop cold rubber polymerization processes where a more powerful initiator (e.g., hydroperoxide) is used. Although dinitrochlorobenzene has been used in cold rubber processes, it has the severe disadvantage of causing discoloration of the rubber; it is also water-insoluble and so toxic as to be a serious health problem to workers in the plant. The alkali metal salts, particularly the sodium salts, of di-lower alkyldithiocarbamates (e.g., sodium dimethyldithiocarbarnate) have been used quite successfully in both hot and cold polymerization recipes, but this compound has the disadvantage of being oxidized to a thiuram disulfide which remains in the finished rubber and causes undesirable and un- Hydroxylamine and hydroxylamine salts such as the sulfate and hydrochloride have also been disclosed as shortstops for pet-sulfate catalyzed emulsion polymerization processes (see U.S.P. 2,444,801), but they are not considered sufficiently effective for commercial use in cold polymerization recipes.

It has now been found surprisingly that N,N-dialkylhydroxylamines are excellent shortstops which are effective for both hot and cold emulsion polymerization processes. In addition, the N,N-dialkylhydroxylamines are significantly more effective than hydroxylamine or its salts. Further, the N,N-dialkylhydroxylamines are nontoxic, are nondiscoloring and have no adverse effect on the processed and cured rubber products in which they are used.

In carrying out the process of this invention, conventional polymerization recipes may be used and the shortstop added in the usual manner. For example, hot synthetic rubber recipes (persulfate or azonitrile initiated) or cold synthetic rubber recipes (hydroperoxide initiated) may be used. The polymerizable material for preparing synthetic rubber latices may be, as is well known, any one or more conjugated diolefins or their admixture with'a copolymerizable monoolefin. The conjugated diolefins are exemplified by the butadienes such as butadiene-l,3, isoprene, chloroprene, cyanobutadiene-l,3, 2-phenylbutadiene, piperylene, 2,3-dimethylbutadiene- 1,3, and the like. The copolymerizable monomer, which will normally comprise up to about of the mixture, will be a monoolefin containing a single CH C group having at least one of the free valence bonds attached to an electronegative group. Such olefins include aryl olefins such as styrene, vinyl naphthalene, a-methyL styrene, p-chlorostyrene, etc.; the tat-methylene carboxylic acids and their esters, amides and nitriles such as acrylic acid, methacrylic acid, acrylonitrile, methacrylamide, and the like. Thus, the synthetic rubber may be any butadiene polymer latex. However, it will be understood that the N,N-dialkylhydroxylamines may also be used in accord with this invention to stop polymerization of other ethylenically unsaturated monomers which yield nonelastomeric latices. Thus, this invention may also be used in the polymerization of vinyl and vinylidene halides (e.g., vinyl chloride, vinylidene fluoride, etc.), acrylates, methacrylates and acrylamides (methyl acrylate, glycidyl methacrylate, methacrylamide, etc.), vinyl esters (e.g., vinyl acetate, etc.), and in fact in any addition polymerization system where polymerization proceeds through a free radical mechanism.

The addition of the shortstop agent will be made after the desired degree of polymerization has occurred. The amount added will be that required to retard or stop the polymerization as desired and the amount is not critical. However, the amount of agent usually used will be between about 0.01 and about 2.0 parts per hundred parts of monomer (p.h.m.) with about 0.05 to about 0.2 p.h.m. being preferred. As little as 0.001 p.h.m. will show the effect, but for practical purposes at least about 0.025 p.h.m. will be used. Using more than 2 p.h.m. is not necessary and is wasteful of material.

The shortstops used in the process of this invention may be any N,N-dialkylhydroxylamine and the term alkyl is meant to include cycloalkyl. Because of availability the N,N-dialkylhydroxylamines containing up to about eighteen carbon atoms in each alkyl group will be used, and each "of the alkyl groups on the nitrogen atom of the hydroxylamine may be different. It is preferred to use those N,N-dialkylhydroxylamines containing up to 6 carbon atoms in each alkyl group and because of cost and availability the most preferred agents are those containing from one to three carbon atoms in each alkyl group. Specific compounds which are operable in this invention include N,N-dimethylhydroxylamine, N,N-diethylhydroxylamine, N,N-di-n-propylhydroxylamine, N,N- diisopropylhydroxylamine, N,N-di-normal butylhydroxylamine, the N,N-diamylhydroxylamines, N,N-dicyclohexylhydroxylamine, N-rnethyl N ethylhydroxylamine, N,N di decylhydroxylamine, N,N-dioctadecylhydroxylamine, N-methyl-N-cyclohexylhydroxylamine and the like. These compounds are known and may be prepared by any one of several known methods as, for example, by converting the appropriate tertiary amine to the amine oxide and pyrolyzing the oxide to the hydroxylamine and olefin as disclosed by Cope et al. in J. Am. Chem. Soc.,

3 4. 79, 964 (1957). The following examples will serve to Example 2. Ht rubber recip'e' l el su ljnte further illustrate the invention: initiated polychloroprene PQLYMERIZATION PROCEDURE The following recipe was polymerized at 40 C.:

The polymerizations were carried out in glass beverage Parts by Weight bottles having a capacity of 220 ml. The bottle was Water placed in a metal guard which was then clamped in a Nancy Wood rosin small wheel-type polymerizer. The wheel of this polym- NaOH erizer rotated in a water bath held at 50i1 C. Per- KZSZOB forated bottle caps were employed to permit sampling m of the recipe and injection of stopping agent into the Dlspersant' bottles by means of a hypodermic needle and syringe. Chloroprene The percent conversion for a given polymerization time *Daxad-ll, polymerized sodium salts of short chain alkyl was determined by measuring total solids of the recipe at naphthalene Sulfonic acidthat particular time, and estimating conversion from a 15 Three sets of experiments were carried out under total solids-conversion straight line relationship. Total identical conditions using no agent, a prior art stopping solids of the recipe was determined by drying a weighed agent, and a N,N-dialkylhy-droxylamine agent. The folsample of the latex in a weighed aluminum dish by means lowing Table II shows the conditions and agents for each of an infrared lamp for about 1 0 minutes followed by set of polymerization runs:

TABLE II Percent Conversion Concentra- Stopping Agent tion (p.h.m.) xvhent At Time After Adding Agent or Added 1 Hour 18 Hours 24 Hours None 60. 4 72. 0 74. 0 Hydroquinone 0.15 59.5 59.3 61.5 61 7 N ,N-Diethylhydroxylamlne 0.15 57. 5 57.4 57.8 57 6 None 39.1 53. 5 72. 3 72 7 Hydroxylamine sulfate 0.15 36. 5 38.3 53.6 54 1 N,N-Diethylhydroxylarnine 0.15 37.2 37.3 37.8 37 8 None 32.9 42.9 65.0 66 o Hydroxylamine sulfate 0.15 33. 3 34 3 46. 6 47 3 N,N-Dimethylhydroxylamine 0. 15 32. 2 32. 2 33. 3 33 8 .a short period of heating in an oven at 70 C. The stop- Example 3.C0ld rubber redipe-Hydr0peroxide with ping agent was added to the polymerization system as a butadiene-styrene (SBR 1500) dilute aqueous solution and the temperature of the polym- Followin the eneral ol merization rocedure the erization was maintained as conversions were determlned g p y p following cold rubber recipe (SBR 1500) was run at 5 C.

at various tunes to test several shortstop agents:

Example I.H0t rubber recipepersulfate with Paris y Weight butadiene-styrene (SBR 1000) Water Rosin acid soap (Dresinate 214) 1.125 The following butadiene-styrene recipe (SBR 1000) 50 Iron sequestrant (Versene Fe 0.005 p was polymerized: N21 PO -12H O 0.075"

7 Parts by weight Dispersant (Daxad-ll) 0.025 Water 45.0 Modifier (tert-dodecyl mercaptan) 0.05 Sodium fatty acid soap 1.18 p-Menth-ane hydroperoxide 0.02 K S O 0.063 FeSO -7H O 0.03 Modifier (tert-dodecyl mercaptan) 0.075 K P O 0.037 Butadiene 18.0 Butadiene 18.0 I Styrene 7.0 Styrene 7.0

' The following Table I shows the results of shortstopping In order to make the test more stringentQthe temperature the polymerization with various agents: of the polymerization was raised to 50 C. one hour after TABLE I Percent Conversion Concentra- Stopping Agent tion Used (p.h.m.) When After After After Stopped 1 Hr. 18 Hrs. 24 Hrs.

P.h.n1.=Parts per .hundred parts monomer.

ic intervals to determine changes and by touch at period in color, surface softness, relative state of cure and The following Table III TABLE III the shortstop was added. illustrates the conditions used and the results obtained:

It isapparent from the above description of the invention and from the experimental data shown that the use of N,N-dialkylhydroxylamines as shortstops in the preparation of synthetic polymers permits excellent control of the polymerization process, providing a sure and efiective means for stopping the process when desired. These and other advantages of the N,N-dialkylhydroxylamines, particularly with regard to (a) their versatility for both hot and cold synthetic rubber recipes, (b) their non-toxic and non-discoloring nature, (c) their effectiveness at low concentration, (d) their compatibility with the finished rubber product, and (e) their innocuous effects on the rubber make it obvious that this invention is a significant advance in the art of polymer science.

I claim:

1. In the process of preparing a synthetic rubber latex by polymerizing a conjugated diolefin by addition through a free radical mechanism and terminating the polymerization by the addition of a stopping agent, the improvement which comprises using as said stopping agent an N,N- dialkylhydroxylamine containing from one to eighteen carbon atoms in each alkyl group.

2. The process of claim 1 wherein the conjugated diolefin is a butadiene.

3. In the process of preparing a butadiene polymer synthetic rubber latex by addition polymerization through a free radical mechanism, the improvement which comprises stopping the polymerization with an N,N-dialT ylhydroxylamine which contains from one to six carbon atoms in each alkyl group.

4. The process of claim 3 wherein the polymer latex is a hot butadiene polymer synthetic rubber latex.

5. The process of claim 3 wherein the polymer latex is a cold butadiene polymer synthetic rubber latex.

6. The process of claim 3 wherein the polymer latex is a hot butadiene-styrene synthetic rubber latex.

7. The process of claim 3 wherein the polymer latex is a cold butadiene-styrene synthetic rubber latex.

8. The process of claim 3 wherein the butadiene polymer is a copolymer of styrene and butadiene.

9. The process of claim 3 wherein the butadiene polymer is polychloroprene.

10. The process of claim 3 wherein the stopping agent is N,N-dimethylhydroxylamine.

11. The process of claim 3 wherein the stopping agent is N,N-diethylhydroxylamine.

12. The process of claim 3 wherein the stopping agent is N,N-diisopropylhydroxylamine.

13. In the process of preparing a synthetic rubber latex by polymerizing a conjugated diolefin by addition polymerization through a free radical mechanism and terminating the polymerization by the addition of a stopping agent, the step which comprises stopping the polymerization with from about 0.01 to about 0.1 part per hundred parts of monomers of an N,N-dialkylhydroxylamine containing from 1 to 6 carbon atoms in each alkyl group.

14. In the process of preparing a cold butadiene-styrene synthetic rubber latex by addition polymerization through a free radical mechanism, the improvement which comprises the step of stopping the polymerization with from about 0.01 to 0.1 part per hundred parts of monomers of an N,N-dialkylhydroxylamine which contains from 1 to 6 carbon atoms in each alkyl group.

15. The process of claim 14 wherein the stopping agent is N,N-diethylhydroxylamine.

References Cited by the Examiner UNITED STATES PATENTS 2,444,801 7/1948 Arundale 26083.3 XR 2,514,363 7/1950 Bancs 26094.6 2,556,651 6/1951 HoWland 260-946 2,965,685 12/1960 Campbell 260-45.8 3,148,225 9/1964 Albert 26094.7

OTHER REFERENCES Bovey et al., Emulsion Polymerization, Interscience, New York, 1955, pages 207, 234-235 relied on.

JOSEPH L. SCHOFER, Primary Examiner. M. LIEBMAN, Examiner. 

1. IN THE PROCESS OF PREPARING A SYNTHETIC RUBBER LATEX BY POLYMERIZING A CONJUGATED DIOLEFIN BY ADDITION THROUGH A FREE RADICAL MECHANISM AND TERMINATING THE POLYMERIZATION BY THE ADDITION OF A STOPPING AGENT, THE IMPROVEMENT WHICH COMPRISES USING AS SAID STOPPING AGENT AN N,NDIALKYLTHYDROXYLAMINE CONTAINING FROM ONE TO EIGHTEEN CARBON ATOMS IN EACH ALKYL GROUP. 